1. Field of the Invention
The present invention relates to an art of transferring a semiconductor processing substrate (hereinafter referred to as a wafer) among the processing chambers and the like of a semiconductor processing apparatus, and more specifically, relates to a method and apparatus for correcting the position of the wafer.
2. Description of the Related Art
In semiconductor device fabrication, it is preferable to connect the processing chambers or the like and have the wafer transferred among the connected processing chambers. Such transfer of the wafer is performed via a vacuum transfer apparatus for transferring the wafer from one inner chamber to another via connecting passages communicating the processing chambers and the buffer chamber which is a vacuum transfer chamber through the inner portions of the side walls of vacuum vessels constituting the vacuum vessel or the vacuum transfer vessel. Generally, the vacuum transfer apparatus is used in cooperation with various wafer processing modules such as a semiconductor etching or ashing system, a material deposition system and a flat panel display fabricating system.
Along with the increasing demands for cleanliness and higher processing accuracy, vacuum transfer apparatuses are being adopted so that a vacuum condition is continued throughout the processes and also between processes. The vacuum transfer apparatus is disposed for example between ports or vessels for receiving wafers and a plurality of processing chambers in which the wafers are actually subjected to processes such as surface etching or film deposition. Through use of a robot arm disposed within the vacuum transfer apparatus, the wafers are transferred and handed over among the vessels and the processing chambers.
On the other hand, some problems have occurred in transferring wafers using such robots. For example, during transfer of a wafer from one chambers such as a load lock chamber to a target location such as another processing chamber, the wafer may not be positioned or aligned appropriately on the desired position at the target location.
Japanese Patent Application Laid-Open Publication No. 2001-210698 (patent document 1) discloses a method of correcting the position of a wafer by providing sensors in the R axis direction (the axis of transfer) to provide a system to correct the position of a wafer when the center of the wafer is not appropriately positioned or aligned.
However, according to the wafer alignment correcting system of the above-mentioned prior art, the methods utilizing sensors disposed in the R axis direction to detect the wafer position or utilizing sensors disposed in the θ axis direction to correct the wafer position had the following drawbacks.    (1) Since the wafer displacement is detected by the sensors and the position of the wafer is corrected before transferring the wafer into the processing chamber, the displacement occurring after the correction of position during the transfer of the wafer cannot be corrected, and the displacement cannot be detected.    (2) If the transfer speed of the wafer is slowed down before the sensor and the speed is maintained slow enough to prevent displacement of the wafer until the wafer reaches the target position, the throughput of the apparatus is deteriorated and the productivity is thereby affected.